In the story "Why is Hubble Important?" we discussed the invention and development of telescopes, and why looking at the Universe from Earth has its problems. Even though I made many discoveries of the Universe, it was an astrophysicist named Lyman Spitzer, Jr. who first proposed putting a long-lived optical telescope above the Earth's atmosphere. That would be a true space observatory. This is the exciting 60-year (1946-2006) history of the Hubble Space Telescope.
Dr. Spitzer studied the gas and dust between the stars, and put forward the idea that the bright stars in spiral galaxies formed from that gas and dust. In 1946, over ten years before the first observatory was launched, Spitzer came up with the idea of a long-term orbiting observatory. He said a telescope in space would reveal much clearer images than any ground-based telescope. It would, he stated, be able to recognize and distinguish a wide range of light wavelengths because it would not have to deal with the blurring effects of our atmosphere.
His paper entitled "Astronomical Advantages of an Extra-Terrestrial Observatory" described the rewards of putting a telescope in space. He would work for the next 45 years to make his vision a reality.
In 1965, the National Academy of Sciences asked Dr. Spitzer to head a committee looking into the possibility of developing a Large Space Telescope. They talked about how it could be launched, how it could be operated for many years, and how it would communicate with scientists on Earth.
A lot of astronomers didn't like the idea of a space telescope and did not cooperate very much. They thought that a space telescope would take away money and support for ground-based astronomy.
Spitzer worked hard to convince the scientists, as well Congress, that placing a large telescope into space would be good for all. Finally, in 1975, NASA, along with the European Space Agency, began developing what would become the Hubble Space Telescope. A few years later the Space Telescope Science Institute (STScI) was formed to operate the satellite and archive the data the telescope would send to Earth. The STScI is located in Baltimore, Maryland.
So what did astronomers think a space telescope needed? Well, that depended on what they wanted to find out. Each question required a different tool to answer.
Scientists decided that five scientific instruments would be initially included on the Hubble Space Telescope, or HST for short. These are the
- Wide Field Planetary Camera 1 (WFPC1)
- Faint Object Camera (FOC)
- Faint Object Spectrograph (FOS)
- Goddard High Resolution Sprectrograph (GHRS)
- High Speed Photometer (HSP).
The telescope pointing system (made up of Fine Guidance Sensors- FGS) essentially provided a sixth instrument which could be used for measuring angles on the sky.
Each instrument had a different purpose and was designed to look at the Universe in a different way than the others. This way, different kinds of data could be received and studied.
The WFPC1 is the main camera and takes most of the pictures. It is designed to look at only a small portion of the sky, but one can build a mosaic of images to construct a single picture of a larger part of the sky. Each servicing mission installed a new and improved WFPC.
Investigation of the Universe begins with investigating light. Remember in the story "Why is Hubble Important?" we saw how a prism refracts light into the colors of the spectrum. Each color represents a different wavelength of light. The Hubble Space Telescope uses special filters to isolate the types of light astronomers are studying.
Hubble's Space Telescope Imaging Spectrograph (STIS) acts like a prism to break up light coming in from objects in the cosmos into separate colors. Spectra of stars recorded with STIS allow an astonomer to determine the types of the stars and to find out what they are made of. Spectra of gaseous nebulae allow one to determine the physical properties of hot, emitting gas clouds. Spectra of quasars allow one to detect absorption lines from galaxies in space and to determine the make up of the galaxies, as is illustrated in the accompanying figure.
As astronomers learn more and more with a given telescope/instrument combination, they often feel the need to put new instruments on telescopes. For HST, an instrument change required sending a new instrument aloft on a space shuttle and having astronauts mount the new instrument; usually one other instrument had to be removed. One such new instrument added on a Hubble Servicing Mission was the Near Infrared Camera and Multi-Object Spectrometer (NICMOS). The camera produces images of objects in the red, just beyond where the eye can see, that allows the discovery of objects in deep space, billions of light years away. These red wavelengths are termed "near-infrared". The instrument has three cameras with different fields of view.
The FOC was made to look closely at one target. It was removed from the HST in 2002 and replaced with the more powerful Advanced Camera for Surveys (ACS). They both allowed Hubble to focus on single stars in distant star clusters.
The Fine Guidance Sensors aim the HST and keep it focused on its target. They do this by locking onto "guide stars" and measuring the position of the telescope relative to the target object being viewed. Repeated visits to the same object sometimes reveal that the object has moved very slightly, an important source of information for astronomers.
In addition to the scientific instruments described above, the HST has equipment and systems to keep it level, keep it flying, allow it to communicate with Earth, and provide power to the instruments.
One main computer handles the gyroscopes. This equipment senses when the telescope is out of position or needs to look in a different direction. The gyroscopes send a command to the reaction wheels to give a "push" or "spin." Each reaction wheel allows the telescope to point in a particular direction. The HST uses a combination of pushes by different wheels to put itself in the right position.
Since the HST is like a robot, it only works when astronomers tell it what to do and when to do it. Astronomers use communication antennae to send instructions to the space telescope computer. This computer gets the instructions to the right instruments, and receives and records the pictures and information. These same antennae then send the data back to Earth where it is eventually relayed to the Space Telescope Science Institute in Baltimore.
Power is supplied through solar arrays that convert the Sun's energy to electricity. Some of the energy is stored in batteries so the HST will still work even when it is in the Earth's shadow.
So the HST had been thought up, designed, and built. It was the size of a school bus: 43 feet wide and weighing almost 25,000 pounds! The space telescope was built as a reflecting telescope that used curved mirrors to focus the light. Astronomers anxiously awaited its launch in 1986.
But the Challenger Space Shuttle disaster in January 1986 grounded all flights until NASA could make sure space flight was safe. Then other missions had to come first. Finally, finally, in April 1990, the HST was loaded into the cargo bay of the Space Shuttle Discovery on mission STS-31.
April 25, 1990: the "Eye in the Sky" was deployed from the Space Shuttle and positioned at an altitude of 353 miles above the Earth, traveling at a speed of 5 miles per second. Instructions were sent, pictures were taken and the data arrived at the Space Telescope Science Institute.
But oh, no! The first image from the HST was not the amazing picture everyone anticipated. It was blurry and indistinct, a little better than the ground based images but not what was expected. How could that be? Scientists all over the world pondered, suggested, discussed and thought. They inspected the design and construction of each camera. They checked that the gyroscopes were holding steady. They looked at the design and construction of the mirrors. And they found the problem.
As you saw in the image of the reflecting telescope, the primary mirrors have to be curved in just the right angle to focus light on the secondary mirror. These primary mirrors had not been shaped correctly. As shown in the figure, the mirror has to be properly shaped to get all of the light rays to the same focus.
Fortunately the astronomers who developed the HST had thought about how they would maintain a space telescope. Even on Earth, telescopes need to be cleaned and adjusted. The HST had been designed so astronauts traveling on the Space Shuttle could repair and update it. Their first mission, it appeared, would be to fix the mirrors.
Corrective lenses were made to fix the HST's mirror. Three years after the telescope had been launched, astronauts installed these "glasses" in front of the instruments inside the HST. They also replaced the Wide Field Planetary Camera with an improved version (WFPC2).
Now things were getting interesting. Scientists all over the world asked to use the Hubble Space Telescope. They had it pointed to look in Earth's backyard, at the planets in our own solar system, at asteroids and comets, and even the Sun. Of course, the telescope was also available to look at distant objects such as nebulae, supernovae and galaxies. There is a lot out there to see and everyone had ideas of what and how each type of object should be studied.
Remember, the HST is only about 400 miles above the Earth. It was not put into orbit to get closer to objects in the Universe. The Universe is too huge for that distance to mean anything. It would be like standing on your toes to see the moon better. But outside the atmosphere, with the gyroscopes holding it steady, the HST looked deeply, very deeply, extremely deeply, into the far reaches of space. And one after another, the pictures dazzled us.
All was going well. For 15 years we were treated to images in their far-reaching splendor, pictures that connected us with the Universe. Each servicing mission added new and improved cameras and instruments. Scientists found new places to look and what they saw astounded us.
After the moon landings of more than 30 years ago, the HST was the most interesting, popular, educational and inspiring space project ever. We looked forward to seeing even more of "what was out there." Perhaps the answers to the questions astronomers had been asking for centuries would be found:
- What's out there in the Universe?
- How did it get there?
- Why does it look that way?
In February 2003, seven astronauts died in the Columbia Shuttle explosion. Once again Shuttle flights were cancelled. Scientists continued to prepare the fourth servicing mission to Hubble, believing that NASA would be able to overcome this tragedy as well.
In January 2004, however, the White House and NASA administrator Sean O'Keefe, announced that NASA would no longer risk astronaut lives to update the Hubble Space Telescope. In fact, the announcement went on, the HST would be abandoned all together. Mechanically it would be de-orbited and guided to splash down in the Pacific Ocean.
The announcement stunned the world. It was as if we had heard a friend was dying. The HST was not just a cold, unfeeling, scientific space project. It had connected with us, to all of us who love space discovery.
The Hubble Space Telescope had touched our souls with its wonderful pictures and important data. It gave us great and inspiring science. Connections like that run strong and deep. Astronomers, scientists, teachers, Congressmen, school children called, wrote and spoke out against the plan to give up on Hubble.
The outcry about abandoning the Hubble Space Telescope was so loud that the head of NASA announced in August 2004 he would investigate other possibilities.
One of those possibilities was a robotic-servicing mission using Dextre, a robot from the Canadian Space Agency. Dextre was originally designed to make repairs at the International Space Station. But NASA believed it could be reprogrammed to work on the Hubble Space Telescope.
Robotic servicing of the HST made sense. Periodic maintenance was the key to Hubble's success. But risking astronaut lives to change batteries did seem short-sighted, and there was little to be learned by having astronauts do something they had done successfully four times before. Here was an opportunity for Hubble to provide the next step in space exploration.
Robotic servicing in space is necessary to the future of science. If Dextre were successful changing the cameras and batteries and replacing the broken gyroscopes, then space exploration could take a giant leap forward. Robotic missions would free Shuttles and astronauts for tasks that could not be done using a robotic mission.
If Dextre was not successful, scientists would learn what the problems were, and Hubble would be no worse off than before. It was a win-win situation.
But Dextre was never given the chance. Before resigning in February 2005, NASA administrator Sean O'Keefe stated that all plans to service the Hubble Space Telescope robotically were being scrapped.
This announcement came as a complete shock. Six months previous the HST engineers had been promised the opportunity to show whether a path-breaking mission to do the job with a robot was possible. NASA's latest change of heart now doomed Hubble to die in orbit around 2008, when its gyroscopes wore out.
In March 2005, President Bush nominated a new NASA administrator, Mike Griffin.
On April 29, 2005 new NASA Administrator Mike Griffin asked engineers at Goddard Space Flight Center to begin preparations for a Space Shuttle servicing mission to Hubble. Griffin said he would reconsider a servicing mission if the next two shuttle missions were to go well.
The first of those two flights, STS-114 in July 2005, was not completely successful. Discovery's external fuel tank lost large pieces of insulating foam, causing NASA to ground the fleet again until the problem was solved. The next flight was not expected before March 2006.
So was this to be the end of the premier scientific facility in human history? Only time could tell.
Hubble is still operational and will continue to take pictures, record data and keep us informed of events in the Universe until, due to old age, it passes away. But oh, what a time we had!
In fact, the repair mission did finally succeed on May 11, 2009 and Hubble is expected to last through the year 2020 .